Computational devices, often called hosts, on the Internet use the Internet Protocol (IP) to route data. Most of these hosts use IPv4, which has an address space that is rapidly becoming exhausted. A method of conserving addresses in the IPv4 address space could help alleviate the shortage, allowing a continuing increase in the number of hosts on the Internet. Hosts using IPv6 addresses most of the time could release IPv4 addresses, freeing them for use by other hosts, without exhausting the IPv6 address space.